Anyone can comment on a bug. Have a simpler test case? Does it
work for you on a different platform? Let us know!
Just going to say 'Me too!'? Don't clutter the database with that please
— but make sure to vote on the bug!

@krackjoe, thanks, but with your patch applied on 5.5.7, this doesn't change the result of provided case.
A simple fix, see "pass-by-ref-proto-check.patch" just make zend_do_perform_implementation_check a little less strict, and consider pass_by_reference as a boolean (so consider 1 and 2 as equivalent, for the proto check).

the patch is correct, what is not correct is the arg info in memcached extension.
however, it is not currently possible to write the arginfo with the current macros, the correct arginfo as it is expected is:
ZEND_BEGIN_ARG_INFO_EX(arginfo_get, 0, 0, 1)
ZEND_ARG_INFO(0, key)
{ "cache_cb", sizeof("cache_cb")-1, NULL, 0, 0, 1, 0},
{ "cas_token", sizeof("cas_token")-1, NULL, 0, 0, 1, 2},
{ "udf_flags", sizeof("udf_flags")-1, NULL, 0, 0, 1, 2}
ZEND_END_ARG_INFO()
To hide the symptoms is not enough, the arg_info must reflect what is actually required, it should be parsed, and have a way to be specified in C correctly.